It is oftentimes desirable to increase the distance into a wellbore or earth formation into which an acidizing solution can act on the formation before it becomes spent, i.e., it is desirable to increase the reaction time of the acid.
Various methods have been utilized to increase the reaction time of various acidizing solutions on acidizable formations. For example, in some instances an emulsion is prepared containing an oil external phase and an acid internal phase. The oil separates the acid from the formation rock and thereby extends the distance into the formation that the emulsion can penetrate before the acid becomes spent. However, several disadvantages are associated with such emulsions. They are usually much more viscous than acid solutions, thus high pumping pressures are needed. Also, the stability of the emulsions are temperature sensitive; such emulsions are hard to prepare; such emulsions may block the pores of the formations and the like.
In another method an anionic surfactant which renders the surface of a formation oil-wet is dispersed into an acidizing formulation, e.g. U.S. Pat. No. 3,319,714. However, it has been discovered that these types of surfactants are not effective in aqueous solutions containing higher concentrations of acids, e.g. 20 per cent or more HCl solutions.